Cathode assembly



TE NING CHIN CATHODE ASSEMBLY 7 Nov. 24, 1959 Filed Oct. 4, 1957INVENTOR. TE NINE [II-1m imwnai M CATHODE ASSEMBLY Te Ning Chin,Lancaster, Pa., assignor to Radio Corporation of America, a corporationof Delaware Application, ctober4, 1951, Serial No. 688,166

2 Claims. (Cl. 313270) tube is a pickup, or camera, tube which isdesigned to be used in a portable television camera for use in a mobiletelevision unit. Aportable camera generally uses tran sis'tori zedcircuit components which are light in weight and low in powerconsumption. In television cameras of this type, the pickup tube'shouldalso be of the efficient, low power input, miniature, lightweighttype. Thus, a srnall,icompact, low wattage cathode is an esscntial partof, such a pickup tube.

It is" therefore an object of this invention to provide a new andimproved cathode structure.

-It-is another object of this invention -to provide an improvedminiature'cathode mount that efliciently uses the input power. 1. 4

-These objects, as well as others, are accomplished in accordance withthis invention by providing a tubular cathode sleeve that is supportedonlyat an end thereof remotefrom the electron emissive area of thecathode. The support structure, whichis-in the shape of a truncated cone cornpactly supports the cathode within a tubular shaped cathodeshield with a maximum efliciency and minimum of heat .loss.

The invention will be ,more clearlyunderstood by reference totheaccompan'ying single sheet of drawings whe in: r

l-lig l is an enlargdplan view, partially in section, of a pickup tubeutilizing this invention, and, Fig. 2 is an enlargedsectional view'ofthe cathode mount shown in Fig. 1.

Referring nowto Fig. -1, there is shown, a pickup tube embodying a"cathode structure in accordance with this invention. .It should beunderstoodthat the invention is equally, applicable to other types oftubes, such as electron beamtubes,'wherein small, efiicient cathodes aredesired, and the pickuprtnbe. 10 is shown merely as an example of a typeof tube whereimthis invention has been foundtobe especially useful. Thetube 10 comprises an evacuated glass. envelope 112 having an electrongun 14 in one end thereof. The electron gun 14, which will be explainedin detail hereinafter, is for the purpose of providing a beam ofelectrons which is controlled and/or accelerated down the tube by acontrol electrode 16, and an accelerating electrode 20 toward a targetelectrode 22. One end of the accelerating electrode 20 is covered by afine mesh screen 21 that is closely spaced adjacent to the targetelectrode 22. The electron beam 1 United States Patent is focused onto,and deflected over, the target electrode 22 in any well-known manner,such as by means-of a focus coil and a deflection yoke, neither of whichis shown for simplicity of illustration.

The target electrode 22 comprises a transparent support member 30, suchas glass, which is shown as the end or face plate of the envelope 12. Onthe inner surface of the transparent support member 30' there is atransparent conductive coating 32 which may comprise a coating of tinchloride or tin oxide. On the surface of c the transparent conductivecoating 32 there is a layer of photoconductive material 34, which may bea ma- 12. The sealing ring 31 is used as a lead-in for the conductivecoating 32 during the operation of the tube 10. The electron gun 14, asshown more clearly in Fig. 2,

includes. a hollow, tubular cathode sleeve 36 which is made of amaterial having low heat conduction properties, such as acobalt-nickel-iron alloy. Press fitted into. and closing one end of thecathode sleeve 36 is a cathode cap 38, which is of a high heatconductivity metal, such as nickel. The cathode cap 38 has a coating ofelectron emissive material on the surface thereof may be a material suchas barium oxide and/ or strontium oxide. The cathode cap 38 contacts thecathode sleeve 36'only in a relatively small area 37, which comprises aprotuberance on the cap member 38 that is press fitted into the cathodesleeve 36. The protuberance may be one'or more small indentationslor, inthe alternative, a bead extending completely around the cap member 38.

The small contact area 37 .results in heat conduction A paths from thecathode cap 38 to the cathode sleeve 36 of an extremely high thermalresistance.

Within thetubular cathode sleeve 36, and closely spaced from the innersurface of the cathode cap 38, is a heater wire 40 which is formed ofany material which A has an appropriate electrical resistance to producerelatively large amounts of heat for a relatively small amount of inputpower. Examples of such resistance materials are tungsten and/ormolybdenum. The turns of the heater wire 40 are within the cap 38 inorder to con-j ,7 centrate the heat in this region.

sections 43 and 47. The support member 42 contacts the cathode sleeveonly at the smaller diameter 43 of the funnel shaped member 42.Thecathode sleeve 36 may he spot welded or press fitted to the cathodesuppo t 2-; 1 unnel shaped support member 42 is made of a material, suchas a .CQbEItrHiCkfil-lIOH alloy,'having low heat conductionproperties.to minimize the heat losses to the other cathode support structures. Thefunnel shaped member 42 is supported, such as by press fitting, at anend47, that is opposite to the end 43 that contacts the cathode member36, by a tubular shaped cathode shield' 44, The' cathode shield 44is'also made of a material hayinglow heat conduction properties, such asa cobalt nickel iron alloy, to minimize heat losses. The cathode shield44 substantially encloses the funnel shaped member 42 and the cathode36. The cathode shield 44 is press fitted into another tubular shapedmember 45 for the purpose of adding rigidity to the cathode mount. Thetubular shaped member 45 may also be a cobaltnickel-iron alloy tominimize heat losses. Another reason for the presence of the tubularshaped member 45 Patented Nov. 24, less mount, could be withdrawn andreplaced by another cathode assembly. a

In addition to the high thermal resistance materials used in the cathodemount members, the members of the cathode mount are machined so as to beas thin as possible, and still provide suitable strength, in order tofurther increase the thermal resistance of the heat conduction pathsaway from thecathode cap 38. Also, due to the geometry of the cathodemount, the heat conduction paths are long, while still within a compactvolume, and therefore the thermal resistance of the heat conductionpaths from the cathode cap is further increased. As an example, thecathode support 42 is joined to the cathode sleeve 36 only adjacent tothe end of the sleeve'36 remote from the electron emissive area, and,the otherend of the cathode support 42 is the only area of the cathodesupport 42 that contacts the cathode shield 45. Thus, the materials,thickness and geometry of the cathode mount are such as to provide anefficient, miniature, heat conserving cathode structure.

The cathode mount assembly shown in Fig. 1 is highly efiicient from aheat radiation standpoint also, in that the funnel shaped support member42 and the cathode shield member 44 are heat reflectors and are providedwith bright inner surfaces to reflect as much heat as possible backtoward the cathode cap 38.

The balance of the electron gun 14 is conventional in that the firstcontrol electrode 16 is positioned adjacent to the cathode cap 38. Theelements of the gun structure 14 are supported by means of glass siderods 46 which are fixed to the particular electrodes in a well-knownmanner.

The cathode mount is extremely small and compact and is highlyeflicient, as was explained, in that the heat generated by the heaterwires 40 is conserved by the compact structure whereby a maximum ofelectron emission is obtained with a minimum heat loss. This eflicient,compact structure is readily adaptable for use in portable televisioncamera tubes, such as the /2" Vidicon type tube.

When the cathode is assembled, the cathode maybe fabricated byconcentric, self-jigging parts, since the parts are substantiallycoaxial, and thus can easily be assembled in a few steps. The junctionsof the various cathode parts may be formed by press fitting or by spotwelding.

A particular example of materials and sizes for use in the cathode mountdescribed is an follows:

Cathode cap 38:

. 4 Cathode shield 44:

Material Nickel-cobalt-iron alloy Length inch .275 Width inch .191Thickness inch .005

Cathode member 45: Q

Material Nickel-cobalt-iron alloy Length in h .216 Diameter inch .201Thickness inch .005

It should be noted'thatthe cathode mount assembly is free of anyinsulating members, such as mica, which is often found in the prior artstructures. The insulating members may tend to cause loose particleswithin the tube 10 by flaking of the insulator during tube processing oroperation. The loose particles are particularly harmful in a pickup tubeif they should land on the photoconductor or on the screen of the finalaccelerating electrode. Also, it should be noted that the cathode mountassembly is made only of metal which may actually be made more heatinsulating than materials that are electrical insulators, 'due to thefact that the metal may be machined to extremely fine thicknesses. Onthe other hand, electrical insulators, e.g., mica, cannot be machined tothese fine thicknesses and still provide adequate support for thecathode mount.

The particular cathode assembly described produces an electron beamsuitable for operation of a television pickup tube with an input powerof approximately 0.6 of a watt. Thus, the low power, compact cathodeassembly I is extremely useful as a cathode in a pickuptube inportable-televisioncameras.

What is claimed is: v

1. A cathode mount assembly comprising a hollow metallic cylindricalcathode sleeve member a metallic cathode cap member closing one end ofsaid sleeve member, electron emissive material on said cap member, ahollow metallic truncated conical support member, the smaller end ofsaid support member engaging the other end of said sleeve member, thelarger end of said support member being arranged around said sleevemember Material Nickel Length inch .040 Width inch .045 Thickness inch.002

Funnel shaped support member 42:

Material Nickel-cobalt-iron alloy Length inch ,177 Large diameter inch.178 Small diameter inch .048 Thickness inch. .001

Length of top and bottom parallel walls inch .019

Cathode sleeve 36:

adjacent to said one end offs'aid sleeve member, a hollow cylindricalmetallic cathode shield spaced concentrically around said supportmember, one end ofsaid cathode shield engaging said larger end of saidsupport member, a cathode lead-in connected to said shield adjacent tothe other end of said shield, and aheater coil within said sleevemember, the turns of said heater coil being concentrated adjacent tosaid one end of said sleeve member; I

. 2. A cathode mount assembly as in claim 1 wherein said metallicmembers have a thickness not greater than .005 inch whereby the heatconductionpaths of said members are of high resistance. l

References Cited in the tile of this patent Great Britain Oct. 24, 1956

